Method of sealing integrated circuits

ABSTRACT

This invention relates to integrated circuits which are protected from the environment. Such circuits are sealed by applying a diffusion barrier metal layer to the bond pads and two passivation layers to the remainder of the circuit.

This is a divisional of copending application(s) Ser. No. 08/023,450filed on Feb. 26, 1993 pending.

BACKGROUND

The present invention relates to integrated circuits which are protectedfrom the environment. These circuits are inexpensive to fabricate andhave improved performance and reliability.

Modern electronic circuits must be able to withstand a wide variety ofenvironmental conditions such as moisture, ions, heat and abrasion. Asignificant amount of work has been reported directed toward variousprotective measures to minimize the exposure of such circuits to theabove conditions and thereby increase their reliability and life.

Many prior art processes for protecting electronic circuits haveinvolved sealing or encapsulating the circuits after they have beeninterconnected. For example, it is known in the art to use materialssuch as silicones, polyimides, epoxies, other organics, plastics, andthe like to encapsulate such interconnected circuits. The abovematerials, however, are of only limited value since most are permeableto environmental moisture and ions.

Similarly, interconnected circuits have also been sealed within ceramicpackages. This process has proven to be relatively effective inincreasing device reliability and is currently used in selectapplications. The added size, weight and cost involved in this method,however, inhibits widespread application in the electronic industry.

The use of lightweight ceramic protective coatings on electronic deviceshas also been suggested. For instance, Haluska et al. in U.S. Pat. Nos.4,756,977 and 4,749,631 describe the use of ceramic silica coatingsderived from hydrogen silsesquioxane and silicate esters, respectively,as well as additional ceramic layers as hermetic barriers. The presentinventor has discovered that when such coatings are applied specificallyto integrated circuits at the wafer stage and even though the bond padsare subsequently opened by removing a portion of the coating, theresultant circuits remain sealed and exhibit increased reliability andlife.

Sealing circuits at the wafer stage is also known in the art. Forexample, it is known in the art to coat fabricated integrated circuitswith ceramic materials such as silica and/or silicon nitride by CVDtechniques. These coatings are then etched back at the bond pads for theapplication of leads. The wafers coated in this manner, however, haveinadequate reliability and life.

Similarly, Byrne in U.S. Pat. No. 5,136,364 teaches a method for sealingintegrated circuits at the wafer stage. The process described thereincomprises applying a first passivation coating which overlaps the edgesof an aluminum bonding pad on an integrated circuit, applying a sequenceof conductive layers comprising a barrier metal layer and a noble metallayer which overlay the aluminum bond pad and which has edges whichoverlap the first passivation layer, and then applying a secondpassivation layer which overlaps the edges of the sequence of conductivelayers. This process, however, is complex and involves manydeposition/etch steps.

The present inventor has now developed a simple process for theprotection of integrated circuits which involves sealing the bond padsof integrated circuits with diffusion barrier layers and sealing theremainder of the device with passivation layers.

SUMMARY OF THE INVENTION

The present invention relates to sealed integrated circuits. Thesecircuits comprise a circuit subassembly having bond pads. A primarypassivation layer covers the surface of this subassembly and openingsare provided therein to expose at least a portion of the top surface ofthese bond pads. A diffusion barrier metal layer covers at least aportion of the top surfaces of the bond pads. A secondary passivationcovers at least the primary passivation and the edges of the diffusionbarrier metal layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a semiconductor device having the primarypassivation, diffusion barrier metal, and secondary passivation of thepresent invention.

FIG. 2 is a cross-section of a semiconductor device having a 2 layerprimary passivation, diffusion barrier metal and the secondarypassivation of the present invention.

FIG. 3 is a cross-section of a semiconductor device having the primarypassivation, diffusion barrier metal and 2 layer secondary passivationof the present invention. This Figure also shows a relocated bond pad.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based on the discovery that integrated circuitscan be sealed by the application of diffusion barrier metal layers overthe bond pads and ceramic layers over the remainder of the circuits. Thediffusion barrier metal layers are corrosion resistant and inhibitcontact of degradative materials with the bond pads. Similarly, thepassivation layers inhibit degration of the remainder of the circuit bylimiting contact with such degradative materials. The resultant sealedcircuits can then be easily interconnected by bonding (eg., TAB,flip-chip, wire bonding, etc. with gold, copper, solder, etc.) to thediffusion barrier metal layer. These circuits are much simpler andcheaper to make than prior art circuits since they don't require sealednoble metal layers. In addition, since this process can be performed atthe wafer stage, production can be simplified and, thus, costs reduced.

The integrated circuit subassemblies used in the process of thisinvention are not critical and nearly any which are known in the artand/or produced commercially are useful herein. The processes used toproduce such circuits are also known and not critical to the invention.Exemplary of such circuits are those comprising a semiconductorsubstrate (eg., silicon, gallium arsenide, etc.) having an epitaxiallayer grown thereon. This epitaxial layer is appropriately doped to formthe PN-junction regions which constitute the active regions of thedevice. These active regions are diodes and transistors which form theintegrated circuit when appropriately interconnected by a properlypatterned metallic layer. This metallic interconnect layer terminates atthe bond pads on the exterior surface of the circuit subassembly. FIG. 1depicts a cross-section of such a semiconductor substrate wherein (1) isthe semiconductor substrate and (2) is the bond pad.

In the process of the present invention, the above integrated circuitsubassemblies are sealed by (1) applying a primary passivation layerover the surface of this subassembly; (2) applying a diffusion barriermetal layer over at least a portion of the top surfaces of the bondpads; and (3) applying a secondary passivation over at least the primarypassivation and the edges of the diffusion barrier metal layer. This isshown in FIG. 1 wherein (3) is primary passivation, (4) is the diffusionbarrier metal and (5) is the secondary passivation.

The method for applying the primary passivation is not critical andnearly any approach can be used. Generally, however, the top surface ofthe subassembly, including the bond pads, is covered with the primarypassivation and then the passivation covering the bond pads is etched.One example of a method for depositing the primary passivation involvesapplying a silicon-containing ceramic material by a process comprisingcoating the circuit with a composition comprising a preceramicsilicon-containing material followed by converting the preceramicsilicon-containing material to a ceramic. Typically, the preceramicsilicon-containing material is converted to a ceramic by heating it to asufficient temperature. This approach is particularly advantageous inthat the resultant coating is planar.

As used in the present invention, the term "preceramicsilicon-containing material" describes material which can be renderedsufficiently flowable to impregnate and coat the surface of a circuitand which can be subsequently converted to a solid layer exhibitingproperties generally recognized by those skilled in the art ascharacteristic of a ceramic. These materials include, for example,precursors to silicon oxides, silicon nitride, silicon oxynitride,silicon oxycarbide, silicon carbonitride, silicon oxycarbonitride,silicon carbide and the like.

The preferred preceramic silicon-containing materials to be used in theprocess of this invention are precursors to silicon oxides, especiallysilica. The silica precursors which may be used in the inventioninclude, but are not limited to, hydrogen silsesquioxane resin(H-resin), hydrolyzed or partially hydrolyzed R_(n) Si(OR)_(4-n), orcombinations of the above, in which each R is independently analiphatic, alicyclic or aromatic substituent of 1-20 carbon atoms,preferably 1-4, such as an alkyl (eg. methyl, ethyl, propyl), alkenyl(eg. vinyl or allyl), alkynyl (eg. ethynyl), cyclopentyl, cyclohexyl,phenyl etc., and n is 0-3, preferably 0 or 1.

H-resin is used in this invention to describe a variety of hydridosilaneresins having units of the structure HSi(OH)_(x) (OR)_(y) O_(z/2) inwhich each R is independently an organic group which, when bonded tosilicon through the oxygen atom, forms a hydrolyzable substituent,x=0-2, y=0-2, z=1-3, and x+y+z=3. These resins may be either fullycondensed (x=0, y=0 and z=3) or they may be only partially hydrolyzed (ydoes not equal 0 over all the units of the polymer) and/or partiallycondensed (x does not equal 0 over all the units of the polymer).Although not represented by this structure, various units of theseresins may have either zero or more than one Si--H bond due to variousfactors involved in their formation and handling. Exemplary ofsubstantially condensed H-resins (less than about 300 ppm silanol) arethose formed by the process of Frye et al. in U.S. Pat. No. 3,615,272which is incorporated herein by reference. This polymeric material hasunits of the formula (HSiO_(3/2))_(n) in which n is generally 8-1000.The preferred resin has a number average molecular weight of from about800-2900 and a weight average molecular weight of between about8000-28,000 (obtained by GPC analysis using polydimethylsiloxane as acalibration standard). When heated sufficiently, this material yields aceramic coating essentially free of SiH bonds.

Exemplary H-resin which may not be fully condensed include those of Banket al. in U.S. Pat. No. 5,010,159, or those of Weiss et al. in U.S. Pat.No. 4,999,397, both of which are incorporated herein by reference.Exemplary H-resin which is not fully hydrolyzed or condensed is thatformed by a process which comprises hydrolyzing a hydrocarbonoxyhydridosilane with water in an acidified oxygen-containing polar organicsolvent.

A platinum, rhodium or copper catalyst may be admixed with the hydrogensilsesquioxane to increase the rate and extent of its conversion tosilica. Any platinum, rhodium or copper compound or complex that can besolubilized in this solution will be operable. For instance, anorganoplatinum composition such as platinum acetylacetonate or rhodiumcatalyst RhCl₃ [S(CH₂ CH₂ CH₂ CH₃)₂ ]₃, obtained from Dow CorningCorporation, Midland, Mich. are all within the scope of this invention.The above catalysts are generally added to the solution in an amount ofbetween about 5 and 500 ppm platinum or rhodium based on the weight ofresin.

The second type of silica precursor material useful herein includeshydrolyzed or partially hydrolyzed compounds of the formula R_(n)Si(OR)_(4-n) in which R and n are as defined above. Some of thesematerials are commercially available, for example, under the tradenameACCUGLASS. Specific compounds of this type includemethyltriethoxysilane, phenyltriethoxysilane, diethyldiethoxysilane,methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane,vinyltrimethoxysilane, tetramethoxysilane, tetraethoxysilane,tetrapropoxysilane, and tetrabutoxysilane. After hydrolysis or partialhydrolysis of these compounds, the silicon atoms therein may be bondedto C, OH or OR groups, but a substantial portion of the material isbelieved to be condensed in the form of soluble Si--O--Si resins.Compounds in which x=2 or 3 are generally not used alone as volatilecyclic structures are generated during pyrolysis, but small amounts ofsaid compounds may be cohydrolyzed with other silanes to prepare usefulpreceramic materials.

In addition to the above SiO₂ precursors, other ceramic oxide precursorsmay also be advantageously used herein either solely or in combinationwith the above SiO₂ precursors. The ceramic oxide precursorsspecifically contemplated herein include compounds of various metalssuch as aluminum, titanium, zirconium, tantalum, niobium and/or vanadiumas well as various non-metallic compounds such as those of boron orphosphorous which may be dissolved in solution, hydrolyzed, andsubsequently pyrolyzed at relatively low temperatures to form ceramicoxides.

The above ceramic oxide precursor compounds generally have one or morehydrolyzable groups bonded to the above metal or non-metal, depending onthe valence of the metal. The number of hydrolyzable groups to beincluded in these compounds is not critical as long as the compound issoluble in the solvent. Likewise, selection of the exact hydrolyzablesubstituent is not critical since the substituents are either hydrolyzedor pyrolyzed out of the system. Typical hydrolyzable groups include, butare not limited to, alkoxy, such as methoxy, propoxy, butoxy and hexoxy,acyloxy, such as acetoxy, other organic groups bonded to said metal ornon-metal through an oxygen such as acetylacetonate or an amino groups.Specific compounds, therefore, include zirconium tetracetylacetonate,titanium dibutoxy diacetylacetonate, aluminum triacetylacetonate,tetraisobutyl titanium and Ti(N(CH₃)₂)₄.

When SiO₂ is to be combined with one of the above ceramic oxideprecursors, generally it is used in an amount such that the finalceramic contains 70 to 99.9 percent by weight SiO₂.

Examples of other silicon-containing preceramic materials includesilicon carbonitride precursors such as hydridopolysilazane (HPZ) resinand methylpolydisilylazane (MPDZ) resin. Processes for the production ofthese materials are described in U.S. Pat. Nos. 4,540,803 and 4,340,619,respectively, both of which are incorporated herein by reference.Examples of silicon carbide precursors include polycarbosilanes andexamples of silicon nitride precursors include polysilazanes. Oxygen canbe incorporated into the ceramics resulting from the above precursors orthe precursors can be converted to silica by pyrolyzing them in anoxygencontaining environment.

The above silicon-containing preceramic material is then used to coatthe integrated circuit. The material can be used in any practical formbut it is preferred to use a liquid comprising the preceramic materialin a suitable solvent. If this solution approach is used, the preceramicliquid is generally formed by simply dissolving or suspending thepreceramic material in a solvent or mixture of solvents. Variousfacilitating measures such as stirring and/or heat may be used to assistin the dissolution/dispersion. The solvents which may be used in thismethod include, for example, alcohols such as ethyl or isopropyl,aromatic hydrocarbons such as benzene or toluene, alkanes such asn-heptane or dodecane, ketones, cyclic dimethylpolysiloxanes, esters orglycol ethers, in an amount sufficient to dissolve or disperse the abovematerials to low solids. For instance, enough of the above solvent canbe included to form a 0.1-85 weight percent solution.

The circuit is then coated with this liquid by means such as spin,spray, dip or flow coating and the solvent is allowed to evaporate. Anysuitable means of evaporation such as simple air drying by exposure toan ambient environment or the application of a vacuum may be used.

Although the above described methods primarily focus on using a solutionapproach, one skilled in the art would recognize that other equivalentmeans (eg., melt impregnation) would also function herein and arecontemplated to be within the scope of this invention.

The preceramic material is then typically converted to thesilicon-containing ceramic by heating it to a sufficient temperature.Generally, the temperature is in the range of about 50 to about 1000° C.depending on the pyrolysis atmosphere and the preceramic compound.Preferred temperatures are in the range of about 50° to about 600° C.and more preferably 50°-400° C. Heating is generally conducted for atime sufficient to ceramify, generally up to about 6 hours, with lessthan about 2 hours being preferred.

The above heating may be conducted at any effective atmospheric pressurefrom vacuum to superatmospheric and under any effective oxidizing ornon-oxidizing gaseous environment such as those comprising air, O₂, aninert gas (N₂, etc.), ammonia, amines, moisture, N₂ O, etc.

Any method of heating such as the use of a convection oven, rapidthermal processing, hot plate, or radiant or microwave energy isgenerally functional herein. The rate of heating, moreover, is also notcritical, but it is most practical and preferred to heat as rapidly aspossible.

Additional examples of methods for the application of the primarypassivation include physical vapor deposition (PVD) or chemical vapordeposition (CVD) of coatings such as silicon oxygen containing coatings,silicon containing coatings, silicon carbon containing coatings, siliconnitrogen containing coatings, silicon oxygen nitrogen coatings, siliconnitrogen carbon containing coatings, silicon oxygen carbon containingcoatings, silicon oxygen carbon nitrogen containing coatings and/ordiamond like carbon coatings.

The materials and methods for the formation of these ceramic coatingsare not critical to the invention and many are known in the art.Examples of applicable methods include a variety of chemical vapordeposition techniques such as conventional CVD, photochemical vapordeposition, plasma enhanced chemical vapor deposition (PECVD), electroncyclotron resonance (ECR), jet vapor deposition, etc. and a variety ofphysical vapor deposition techniques such as sputtering, electron beamevaporation, etc. These processes involve either the addition of energy(in the form of heat, plasma, etc.) to a vaporized species to cause thedesired reaction or the focusing of energy on a solid sample of thematerial to cause its deposition.

In conventional chemical vapor deposition, the coating is deposited bypassing a stream of the desired precursor gases over a heated substrate.When the precursor gases contact the hot surface, they react and depositthe coating. Substrate temperatures in the range of about 100-1000° C.are sufficient to form these coatings in several minutes to severalhours, depending on the precursors and the thickness of the coatingdesired. If desired, reactive metals can be used in such a process tofacilitate deposition.

In PECVD, the desired precursor gases are reacted by passing themthrough a plasma field. The reactive species thereby formed are thenfocused at the substrate and readily adhere. Generally, the advantage ofthis process over CVD is that lower substrate temperature can be used.For instance, substrate temperatures of about 20° up to about 600° C.are functional.

The plasma used in such processes can comprise energy derived from avariety of sources such as electric discharges, electromagnetic fieldsin the radio-frequency or microwave range, lasers or particle beams.Generally preferred in most plasma deposition processes is the use ofradio frequency (10 kHz-10² MHz) or microwave (0.1-10 GHz) energy atmoderate power densities (0.1-5 watts/cm²). The specific frequency,power and pressure, however, are generally tailored to the precursorgases and the equipment used.

Examples of suitable processes for the deposition of the siliconcontaining coating described above include (a) the chemical vapordeposition of a silane, halosilane, halodisilane, halopolysilane ormixtures thereof, (b) the plasma enhanced chemical vapor deposition of asilane, halosilane, halodisilane, halopolysilane or mixtures thereof, or(c) the metal assisted chemical vapor deposition of a silane,halosilane, halodisilane, halopolysilane or mixtures thereof.

Examples of suitable processes for the deposition of the silicon carboncontaining coating described above include (1) the chemical vapordeposition of a silane, alkylsilane, halosilane, halodisilane,halopolysilane or mixtures thereof optionally in the presence of analkane of one to six carbon atoms or an alkylsilane, (2) the plasmaenhanced chemical vapor deposition of a silane, alkylsilane, halosilane,halodisilane, halopolysilane or mixtures thereof optionally in thepresence of an alkane of one to six carbon atoms or an alkylsilane or(3) the plasma enhanced chemical vapor deposition of a silacyclobutaneor disilacyclobutane as further described in U.S. Pat. No. 5,011,706,which is incorporated herein in its entirety.

Examples of suitable processes for the deposition of the silicon oxygencarbon containing coating described above include (1) the chemical vapordeposition of a silane, alkylsilane, halosilane, halodisilane,halopolysilane or mixtures thereof optionally in the presence of analkane of one to six carbon atoms or an alkylsilane and further in thepresence of an oxidizing gas such as air, oxygen, ozone, nitrous oxideand the like, (2) the plasma enhanced chemical vapor deposition of asilane, alkylsilane, halosilane, halodisilane, halopolysilane ormixtures thereof optionally in the presence of an alkane of one to sixcarbon atoms or an alkylsilane and further in the presence of anoxidizing gas such as air, oxygen, ozone, nitrous oxide and the like or(3) the plasma enhanced chemical vapor deposition of a silacyclobutaneor disilacyclobutane as further described in U.S. Pat. No. 5,011,706,which is incorporated herein in its entirety, in the presence of anoxidizing gas such as air, oxygen, ozone, nitrous oxide and the like.

Examples of suitable processes for the deposition of the siliconnitrogen containing coating described above include (A) the chemicalvapor deposition of a silane, halosilane, halodisilane, halopolysilaneor mixtures thereof in the presence of ammonia, (B) the plasma enhancedchemical vapor deposition of a silane, halosilane, halodisilane,halopolysilane, or mixtures thereof in the presence of ammonia, (C) theplasma enhanced chemical vapor deposition of a SiH₄ --N₂ mixture such asthat described by Ionic Systems or that of Katoh et al. in the JapaneseJournal of Applied Physics, vol. 22, #5, pp1321-1323, or (D) reactivesputtering such as that described in Semiconductor International, p 34,August 1987.

Examples of suitable processes for the deposition of the silicon oxygennitrogen containing coating described above include (A) the chemicalvapor deposition of a silane, halosilane, halodisilane, halopolysilaneor mixtures thereof in the presence of ammonia and an oxidizing gas suchas air, oxygen, ozone, nitrous oxide and the like, (B) the plasmaenhanced chemical vapor deposition of a silane, halosilane,halodisilane, halopolysilane, or mixtures thereof in the presence ofammonia and an oxidizing gas such as air, oxygen, ozone, nitrous oxideand the like, (C) the plasma enhanced chemical vapor deposition of aSiH₄ --N₂ mixture such as that described by Ienic Systems or that ofKatoh et al. in the Japanese Journal of Applied Physics, vol. 22, #5,pp1321-1323 in the presence of an oxidizing gas such as air, oxygen,ozone, nitrous oxide and the like, or (D) reactive sputtering such asthat described in Semiconductor International, p 34, August 1987 in thepresence of an oxidizing gas such as air, oxygen, ozone, nitrous oxideand the like.

Examples of suitable processes for the deposition of the silicon oxygencontaining coating described above include (A) the chemical vapordeposition of a silane, halosilane, halodisilane, halopolysilane ormixtures thereof in the presence of an oxidizing gas such as air,oxygen, ozone, nitrous oxide and the like, (B) the plasma enhancedchemical vapor deposition of a silane, halosilane, halodisilane,halopolysilane, or mixtures thereof in the presence of an oxidizing gassuch as air, oxygen, ozone, nitrous oxide and the like, (c) the chemicalvapor deposition or plasma enhanced chemical vapor deposition oftetraethylorthosilicate, methyltrimethoxysilane,methylhydrogensiloxanes, dimethylsiloxanes and the like in the presenceof an oxidizing gas such as air, oxygen, ozone, nitrous oxide and thelike, or (d) the chemical vapor deposition or plasma enhanced chemicalvapor deposition of hydrogen silsesquioxane resin in the presence of anoxidizing gas such as air, oxygen, ozone, nitrous oxide and the like asdescribed in U.S. Pat. No. 5,165,955, which is incorporated herein byreference.

Examples of suitable processes for the deposition of the silicon carbonnitrogen containing coating described above include (i) the chemicalvapor deposition of hexamethyldisilazane, (ii) the plasma enhancedchemical vapor deposition of hexamethyldisilazane, (iii) the chemicalvapor deposition of silane, alkylsilane, halosilane, halodisilane,halopolysilane or mixture thereof optionally in the presence of analkane of one to six carbon atoms or an alkylsilane and further in thepresence of ammonia, or (iv) the plasma enhanced chemical vapordeposition of a silane, alkylsilane, halosilane, halodisilane,halopolysilane or mixture thereof optionally in the presence of analkane of one to six carbon atoms or an alkylsilane and further in thepresence of ammonia.

Examples of suitable processes for the deposition of the silicon oxygencarbon nitrogen containing coating described above include (i) thechemical vapor deposition of hexamethyldisilazane in the presence of anoxidizing gas such as air, oxygen, ozone, nitrous oxide and the like,(ii) the plasma enhanced chemical vapor deposition ofhexamethyldisilazane in the presence of an oxidizing gas such as air,oxygen, ozone, nitrous oxide and the like, (iii) the chemical vapordeposition of silane, alkylsilane, halosilane, halodisilane,halopolysilane or mixture thereof optionally in the presence of analkane of one to six carbon atoms or an alkylsilane and further in thepresence of ammonia and an oxidizing gas such as air, oxygen, ozone,nitrous oxide and the like, or (iv) the plasma enhanced chemical vapordeposition of a silane, alkylsilane, halosilane, halodisilane,halopolysilane or mixture thereof optionally in the presence of analkane of one to six carbon atoms or an alkylsilane and further in thepresence of ammonia and an oxidizing gas such as air, oxygen, ozone,nitrous oxide and the like.

Examples of suitable processes for the deposition of the diamond-likecarbon coating described above include exposing the substrate to anargon beam containing a hydrocarbon in the manner described in NASA TechBriefs, November 1989 or by one of the methods described by Spear in J.Am. Ceram. Soc., 72, 171-191 (1989).

It should be noted that the primary passivation may be doped with otheragents, if desired. For instance, the coatings may be doped with boron,phosphorous, or carbon to modify its characteristics.

Either one or more of the above coatings may be used as the primarypassivation. In a preferred embodiment of the invention, asilicon-containing ceramic layer derived from a preceramicsilicon-containing material is used as a first planar layer and a secondlayer of a material such as silicon nitride or silicon carbide isapplied on top of the first layer by CVD. FIG. 2 depicts a cross-sectionof such a semiconductor substrate (1) having a bond pad (2), a primarypassivation comprising a silicon containing ceramic layer derived from apreceramic silicon containing material (3a) and layer applied by CVD(3b), a barrier metal (4) and the secondary passivation layer (5).

If the standard approach is utilized, the coating covering the bond padis etched or partially etched to expose the top surface of the bond padfor deposition of the diffusion barrier metal layer. In one embodimentof the invention, the primary passivation on the entire top surface ofthe bond pad can be removed. In the preferred embodiment, however, onlya portion of the primary passivation on the top surface of bond pad isremoved such that the primary passivation overlaps the edges and the topsurface of the bond pad. It should be noted, however, that otherapproaches which result in open bond pads may also be used (eg.,depositing the coating only around the bond pads).

The method of etching is not critical and nearly any process known inthe art will function herein. This includes, for example, dry etching(eg., with plasma), wet etching (eg., with aqueous hydrofluoric acid)and/or laser ablation.

It should be noted that circuits having a primary passivation andmethods for their manufacture are known in the art. For instance, it isknown to apply a primary passivation comprising one or more ceramiccoatings of silica, silicon nitride or silicon oxynitride by a chemicalvapor deposition technique employing precursors such as silane andoxygen, nitrous oxide, nitrogen, and ammonia. Similarly, it is known inthe art to etch these coatings to expose the bond pads forinterconnection. What has not been described in this prior art, however,is the deposition of a diffusion barrier metal layer and a secondarypassivation on such circuits.

The diffusion barrier metal layer useful herein is not critical and isgenerally known in the art for use within integrated circuits forbuilding the multiple layers of the circuit. Generally, such a layercomprises one or more coatings of metals and metal alloys such astungsten, titanium-tungsten, titanium-nitride, nickel-vanadium,chromium, nickel-chromium, and the like.

The method for forming the diffusion barrier metal layer is also notcritical and many techniques are known in the art. Examples of suchprocesses include various physical vapor deposition (PVD) techniquessuch as sputtering and electron beam evaporation. A common approachinvolves sputtering the barrier metal layer on the surface of thecircuit followed by etching to define the area of the barrier metalcoverage.

The diffusion barrier metal layer may be applied in nearly any geometricconfiguration desired. In a preferred embodiment of the invention, thediffusion barrier metal layer overlaps the first passivation layer toprovide additional protection. This is shown in FIGS. 1, 2, and 3wherein the barrier metal (4) overlaps the primary passivation (3). In asecond preferred embodiment, the diffusion barrier metal layer is usedto relocate the bond pad to an area which is not vertically above theoriginal bond pad. This is shown in FIG. 3 wherein opening (6) is etchedin the secondary passivation at a location not directly above theoriginal bond pad (2).

After the bond pads have been sealed with diffusion barrier metal layer,a secondary passivation comprising one or more additional ceramic layersis applied to the circuit. This secondary passivation is applied in amanner such that the primary passivation and the edges of the diffusionbarrier metal layer are covered. In a preferred embodiment, thesecondary passivation layer also overlaps the top surface or thediffusion barrier metal layer. FIG. 2 depicts a cross-section of such asemiconductor substrate (1) having a bond pad (2), a primary passivation(3), a barrier metal (4) and a secondary passivation layer whichoverlaps the top surface of the barrier metal comprising a siliconcontaining ceramic layer derived from a perceramic silicon containingmaterial (5a) and layer applied by CVD (5b).

The secondary passivation and its method of application are essentiallyidentical to those of the primary passivation described above. Thislayer seals any pores, pinholes and defects in the primary passivationand it seals the edges of the barrier diffusion metal layer to insure acomplete seal.

Generally, the seconday passivation is applied to the entire top surfaceof the circuit including the primary passivation and the diffusionbarrier metal layer. After application, the coating covering thediffusion barrier metal layer is etched or partially etched to allow forattachment of leads. The methods of etching are essentially as describedabove. It should again be noted that alternative means of applying thesecondary passivation may be used.

After the secondary passivation covering the bond pads has been etched,the circuits are heremetically sealed such that they can be handledand/or transported without damage. In addition, either of thepassivation layers may absorb UV or visible light to prevent damage andinhibit inspection. Moreover, circuits sealed in this manner areextremely flexible in methods for interconnection. For instance, bumpsof gold, copper, solder or the like can be applied to the circuit foruse in "flip-chip" or TAB interconnection. Alternatively, leads can bebonded to the diffusion barrier metal layer or silver filled epoxyinterconnects can be formed. This flexible approach is much moredesirable than alternative designs in which noble metals are required.

After interconnection, the device can also be packaged by conventionaltechniques known in the art. For instance, the device can be embeddedwithin an organic encapsulant such as a polyimide, an epoxy orPARYLENE™, it can be embedded within a silicone encapsulant or it can beincluded in a plastic package for additional protection.

That which is claimed is:
 1. A method for sealing an integrated circuitsubassembly having bond pads consisting essentially of;applying aprimary passivation layer comprising at least one coating selected fromthe group consisting of silicon oxides, silicon nitride, siliconoxynitride, silicon oxycarbide, silicon carbonitride, siliconoxycarbonitride and silicon carbide over the surface of the subassemblyand the bond pads; etching the primary passivation to expose at least aportion of the top surface of the bond pads; applying a diffusionbarrier metal layer selected from the group consisting of titanium,titanium-tungsten, titanium-nitride, nickel-vanadium, chromium, andnickel-chromium over at least a portion of the top surfaces of the bondpads exposed through the primary passivation; applying a secondarypassivation comprising at least one coating selected from the groupconsisting of silicon oxides, silicon nitride, silicon oxynitride,silicon oxycarbide, silicon carbonitride, silicon oxycarbonitride andsilicon carbide over the primary passivation and the diffusion barriermetal layer; and etching the secondary passivation to expose at least aportion of the top surfaces of the diffusion barrier metal layer.
 2. Themethod of claim 1 wherein the primary passivation layer is doped with anagent selected from the group consisting of boron, phosphorus andcarbon.
 3. The method of claim 1 wherein the primary passivation layeris deposited by coating the circuit with a composition comprising apreceramic silicon-containing material followed by converting saidmaterial to a ceramic.
 4. The method of claim 1 wherein the primarypassivation is applied by a process selected from the group consistingof physical vapor deposition and chemical vapor deposition.
 5. Themethod of claim 3 wherein the preceramic silicon-containing material ishydrogen silsesquioxane resin.
 6. The method of claim 1 wherein theprimary passivation layer comprises a silicon oxide coating covered byat least one coating selected from the group consisting of SiO₂coatings, SiO₂ /ceramic oxide coatings, silicon coatings, silicon carboncontaining coatings, silicon nitrogen containing coatings, siliconoxygen nitrogen containing coatings, silicon carbon nitrogen containingcoatings and diamond-like carbon coatings.
 7. The method of claim 1wherein the secondary passivation layer is deposited by coating thecircuit with a composition comprising a preceramic silicon-containingmaterial followed by converting said material to a ceramic.
 8. Themethod of claim 1 wherein the secondary passivation is applied by aprocess selected from the group consisting of physical vapor depositionand chemical vapor deposition.
 9. The method of claim 7 wherein thepreceramic silicon-containing material is hydrogen silsesquioxane resin.10. The method of claim 1 wherein the secondary passivation layercomprises a silicon oxide coating covered by at least one coatingselected from the group consisting of SiO₂ coatings, SiO₂ /ceramic oxidecoatings, silicon coatings, silicon carbon containing coatings, siliconnitrogen containing coatings, silicon oxygen nitrogen containingcoatings, silicon carbon nitrogen containing coatings and diamond-likecarbon coatings.